Multiple Spanning Tree Protocol (MSTP) allows packets in different VLANs to be forwarded by using different spanning tree instances, as shown in Figure 1. The configurations are as follows:
All devices on the network belong to the same Multiple Spanning Tree (MST) region.
VLAN 10 packets are forwarded within MSTI 1; VLAN 30 packets are forwarded within MSTI 3; VLAN 40 packets are forwarded within MSTI 4; VLAN 20 packets are forwarded within MSTI 0.
On the network shown in Figure 1, Device A and Device B are aggregation-layer devices, and Device C and Device D are access-layer devices. VLAN 10 and VLAN 30 are terminated on aggregation-layer devices, and VLAN 40 is terminated on an access-layer device. Therefore, Device A and Device B can be configured as the roots of instances 1 and 3 respectively; Device C can be configured as the root of instance 4.